It is my understanding that O Sensei's use of the term 'Aiki' stemmed from his Omoto Kyo experiences; i.e. a mystical concept that suggests some kind of union or coming together of oneself with the universe. It is interesting to attempt to define 'Aiki' from a martial viewpoint, but it is also worth considering that the Founder himself might have defined it primarily from a religious or spiritual viewpoint.